Just found a new source of music to work by... internet radio station Groovera. They have three channels in the chilled-out realm, and I found it when I inexplicably couldn't connect to my old standby, Afternoon Nap. Right now I'm listening to Groovera's Jet City Lounge stream.
Downtempo music isn't always right for me, but it has been for a few years. As I'm sure I've said before: it's about whatever magically optimal level and type of stimulation/background works for you. The key for me is to find the right mood, the right groove, while quieting the mind enough to focus in on what I'm doing.
What music works for you when you're working? Please share in the comments because I want more ideas!